It would involve:
1) Updating the hidden form element names on the confirm page
2) Updating the form action on the confirm page
3) Creating an IPN page that repopulates the cart
4) Deleting the paypal functionality from the confirm page
5) Copy and paste the email and database functionality to the IPN page
This is not directly supported currently, so it should really only be attempted if you have some experience with how payments standard and IPN work.
I'm in the middle of doing this but IPN is asynchronous and recommended only for back office. I'm going to populate the cart based on session variables or maybe not at all. I'm providing order details in account history.